Process for oxidizing a normally gaseous hydrocarbon



March 27, 1962 C. R. MURPHY PROCESS FOR OXIDIZING A NORMALLY GASEOUS HYDROCARBON Filed June 22, 1959 3,027,411 Paocnss ron oxrnizING A NoRMALLY ohsnous HvnnocAanoN This invention relates to a process for the controlled oxidation of normally gaseous hydrocarbons and more particularly to a process for the controlled oxidation of normally gaseous hydrocarbons to obtain a desired product distribution.

Normally gaseous hydrocarbons can be subjected to partial oxidation to produce a mixture of oxygenated products having a lower carbon number than the hydrocarbon charge. While a large variety of oxygenated products are obtained in such oxidation, the principal ones produced are formaldehyde, acetaldehyde and methanol. Care must be taken in such oxidation to maintain the oxygen-hydrocarbon ratio in the charge below the explosive limits for this type of mixture. This can be done, for example, by employing air as the oxidizing medium, the nitrogen in the air serving as a diluent. The presence of nitrogen in the system, however, causes an additional complication to an already complex product recovery system and additionally contributes to vapor losses of the important oxygenated products produced in the oxidation process.

This diiculty can be avoided by employing substantially pure oxygen as the oxidizing medium in the process. In order to avoid the explosive limits for this type of reaction, the amount of oxygen introduced into the oxidation reactor relative to the normally gaseous hydrocarbon must be maintained low. Even when all of the oxygen introduced into the reactor is consumed, a large amount of unreacted hydrocarbon is removed from the reaction zone with the oxygenated products. This, of course, necessitates the separation of a large amount of hydrocarbon from the oxygenated products and the recycle thereof to the reaction zone. This can be done, for example, by recycling the unreacted hydrocarbon and combining therewith suiiicient additional hydrocarbon and oxygen to obtain the desired hydrocarbonoxygen ratio in the charge. The resultant charge is then v preheated and passed to the oxidation Zone.

I have found that a desired product distribution favoring the formation of formaldehyde over acetaldehyde can be obtained in such process by preheating the unreacted hydrocarbon recycle gas, adding to the preheated unreacted recycle hydrocarbon gas a mixture containing fresh hydrocarbon gas and oxygen so that the resultant mixture contains hydrocarbon gas and oxygen in a predetermined ratio and thereafter charging said resultant mixture to an oxidation zone to obtain an oxidized mixture comprising formaldehyde, acetaldehyde and methanol. By operating in accordance with the process of this invention the formation of formaldehyde relative to acetaldehyde is favored.

The process of this invention can be further illustrated by reference to the accompanying llow diagram. A normally gaseous hydrocarbon recycle gas in line 2, which can be at a temperature of about 100 to about 700 F., preferably about 600 to about 650 F., and a pressure of about to about 200 pounds per square inch gauge, preferably about 100 to about 150 pounds per square inch gauge, is passed through preheater 4 wherein the recycle gas is raised to a temperature of about 600 to about 800 F., preferably about 650 to about 750 F., and a pressure of about 0 to about 200 pounds per 3,027,411 Patented Mar. 27, 1962 square inch gauge, preferably about 100 to about 150 pounds per square inch gauge. Normally the amount of time required to obtain the desired temperature rise in the preheater is about 0.1 to about 2.0 seconds, preferably about 0.75 to about 1.5 seconds. The purpose of the preheater in this type of oxidation reaction is to raise the temperature of the bulk of the gas stream to reaction temperature and to allow for an induction period to occur prior to the onset of the oxidation reaction.

In accordance with the process of this invention, the preheated recycle gas as it leaves preheater 4 by line 6 is admixed with a mixture containing the same normally gaseous hydrocarbon being recycled and oxygen from line 8. The hydrocarbon can be ethane, propane, butane or mixtures thereof. The mixture in line 8 is not preheated and is at a temperature of about 60 to about 100 F., preferably about to about 100 F., and a pressure of about 0 to about 200 pounds per square inch gauge, preferably about to about 150 pounds per square inch gauge. The amount of gaseous components added to line 6 from line 8 is normally dependent upon the ratio of gaseous hydrocarbon and oxygen desired in the nal charge mixture. Referred to the pressure and temperature of the preheated recycle hydrocarbon gas, the amount of fresh hydrocargon gas introduced therein by line 8 is about 2 to about 12, preferably about 4 to about 6 percent by volume, and the oxygen introduced therein about one to about 6, preferably about 2 to about 4, percent by volume based on the preheated recycle gas in line 6. The resultant mixture in line 6 is at a temperature of about 550 to about 750 F. preferably about 650 to about 700 F., and a pressure of about 0 to about 200 pounds per square inch gauge, preferably about 100 to about 150 pounds per square o inch gauge.

The resultant gaseous mixture, in line 6 is thereafter passed to reactor 10 wherein the partial oxidation reaction takes place. In order to consume all of the oxygen in the gaseous mixture being introduced into reactor 10 and at the same time reduce the amount of decomposition and degradation products in the desired oxygenater product, the temperature of the reaction therein is desirably maintained at about 650 to about 850 F., preferably about 650 to about 750 F., the pressure about 0 to about 200 pounds per square inch gauge, preferably about 100 to about 150 pounds per square inch gauge, and the contact time, at such conditions, about 0.1 to about 2 seconds, preferably about 0.5 to about one second.

The oxygenated products are removed. from reactor 10 by line 12 and within about 0.1 to about 2 seconds are cooled to a temperature of about 250 to about 500 F., preferably about 300 to about 350 F., and a pres-` sure of about 0 to about 200 pounds per square inch gauge, preferably about 100 to about 150 pounds per square inch gauge, lby passing the same through heat exchanger 14 or any other suitable means. The cooled product in line 16 is thereafter passed to any suitable or conventional recovery means to recover and separate the desired oxygenated compounds, such as formaldehyde, acetaldehyde and methanol, `and unreacted hydrocarbon therefrom. The recovered unreacted gaseous hydrocarbon is recycled by means of line 2. Desirably, the recovered unreacted gaseous hydrocarbon gas is iirst passed by line 18 through heat exchanger 14 for the purpose previously defined prior to recycling by line 2.

The following examples illustrate the fact that reaction conditions remaining constant, the distribution of form` aldehyde and acetaldehyde in the oxygenated product is profoundly affected by the point of addition of fresh gaseous hydrocarbon and oxygen to the system.

3 EXAMPLE I 70 cubic feet of recycle gas at a temperature of 625 F. and a pressure of 160 pounds per square inch gauge analyzing 70 percent by volume propane and 30 percent by volume of methane, ethane, carbon monoxide, carbon dioxide and nitrogen were admixed with 6.3 cubic feet of a fresh mixture containing 70 percent by volume of propane and 30 percent by volume of oxygen, said latter mixture being at atemperature of 100 E. and 100 pounds per square inc h gauge. The resutlant mixture was preheated t a temperature of 650 F. and a pressure of 100 pounds per square inch gauge and then reacted at a temperature of 775 F. and a pressure of 100 pounds per square inch gauge for 0.75 seconds. After cooling the products to a temperature of 325 F. within one second, the oxygenated products were sent to a recovery and separation system.

EXAMPLE 1I In this run, which was carried out in accordance with the process of this invention, the conditions of Example I were maintained with the exception that the fresh mixture of propane and oxygen was added to the recycle propane gas after the latter had been preheated to the stated temperature. The results obtained vin Examples and II are ,set forth below in Table I.

t1 0 2 to C4 alcohols, acetone, dimethyl acetal, methyl formate, Ymcthylal, e c.

A study of the data in Table l reveals the fact that the mere expedient of introducing the fresh gaseous hydrocarbon and oxygen into the system after the recycle hydrocarbon gas has been preheated to reaction temperature, and not before, results in a signicant change in the nature of the oxidation product obtained. Note that this expedient results in an increase of formaldehyde from 26.3 to 33.4 percent by weight and a decrease in the percent of acetaldehyde from 30.7 to 24.8 percent by weight. Since the amount of methanol in each case is about the same, the increase in the amount of formaldehyde obtained cannot be explained on the basis of the conversion of methanol to formaldehyde.

Obviously many modifications and Variations of the in.- vention, as hereinabove set forth, can be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

`I claim:

1. A process for oxidizing a normally gaseous hydrocarbon which comprises subjecting said hydrocarbon in admixture with oxygen to oxidation at a temperature of about 650 to about 850 F. and a pressure of about 0 to about 200 pounds per square inch gauge for about 0.1 to about 2 seconds to produce an oxygenated product predominating in formaldehyde and acetaldehyde and unreacted gaseous hydrocarbon, separating unreacted gaseous hydrocarbon from said oxygenated product, preheating said unreacted gaseous hydrocarbon to a temperature of about 600 to about 800 F. and a pressure of about 0 to about 200 pounds per square inch gauge, admixing with said preheated gaseous hydrocarbon fresh gaseous hydrocarbon and oxygen, and thereafter subjecting the resulting mixture to the aforesaid oxidation reaction, whereby the ratio of formaldehyde to acetaldehyde produced is increased.

12. The process of claim 1 wherein the normally gaseous hydrocarbon is propane.

3. A process for oxidizing a normally gaseous hydrocarbon which comprises subjecting said hydrocarbon in admixture with oxygen to oxidation at a temperature of about 650 to about 850 F. and a pressure of about 0 to about 200 pounds per square inch gauge for about 0.1 to about 2 seconds to produce an oxygenated product predominating in formaldehyde and acetaldehyde and unreacted gaseous hydrocarbon, separating unreacted gaseous hydrocarbon from said oxygenated product, preheating said unreacted gaseous hydrocarbon to a temperature of about 600 to about 800 F. and a pressure of about 0 to about 200 pounds per square inch gauge, adrnixing with said preheated gaseous hydrocarbon about 2 to about 12 percent by volume of fresh gaseous hydrocarbon and about one to about 6 percent by volume of fresh oxygen, and thereafter subjecting the resulting mixture to the aforesaid oxidation reaction, whereby the ratio of formaldehyde to acetaldehyde produced is increased.

4. The process of claim 3 wherein the normally gaseous hydrocarbon is propane.

5. A process for oxidizing a normally gaseous hydrocarbon which comprises subjecting said hydrocarbon in admixture with oxygen to oxidation at a temperature of about 650 to about 850 F. and a pressure of about O to about 200 pounds per square inch gauge for about 0.1 to about 2 seconds to produce an oxygenated product predominating in formaldehyde and acetaldehyde and unreacted gaseous hydrocarbon, separating unreacted gaseous hydrocarbon from said oxygenated product, preheating said unreacted gaseous hydrocarbon to a temperature of about 600 to about 800 F. and a pressure of about 0 to about 200 pounds per square inch gauge, admixing with said preheated gaseous hydrocarbon about 2 to about 12 percent by volume of fresh gaseous hydrocarbon and about one to about 6 percent by volume of fresh oxygen, said fresh gaseous hydrocarbon and fresh oxygen being at a temperature of about 60 to about 100 F. and a pressure of about 0 to about 200 pounds per square inch gauge, and thereafter subjecting the resulting mixture to the aforesaid oxidation reaction, whereby the ratio of formaldehyde to acetaldehyde produced is increased.

6. The process of claim 5 wherein the normally gaseous hydrocarbon is propane.

References Cited in the file of this patent UNITED STATES PATENTS `1,729,711 Curme Oct. 1, 1929 1,995,991 Lenher Mar. 26, 1935 2,186,688 Walker Jan. 9, 1940 2,365,851 Thomas Dec. 26, 1944 2,376,668 Derby May 22, 1945 2,570,215 Dice Oct. 9, 1951 

1. A PROCESS FOR OXIDIZING A NORMALLY GASEOUS HYDROCARBON WHICH COMPRISES SUBJECTING SAID HYDROCARBON IN ADMIXTURE WITH OXYGEN TO OXIDATION AT A TEMPERATURE OF ABOUT 650* TO ABOUT 850*F. AND A PRESSURE OF ABOUT 0 TO ABOUT 200 POUNDS PER SQUARE INCH GAUGE FOR ABOUT 0.1 TO ABOUT 2 SECONDS TO PRODUCE AN OXYGENATED PRODUCT PREDOMINATING IN FORMALDEHYDE AND ACERALDEHYDE AND UNREACTED GASEOUS HYDROCARBONS, SEPARATING UNREACTED GASEOUS HYDROCARBONS FROM SAID OXYGENATED PRODUCT, PREHEATING SAID UNREACTED GASEOUS HYDROCARBONS TO A TEMPERATURE OF ABOUT 600* TO ABOUT 800*F. AND A PRESSURE OF ABOUT 0 TO ABOUT 200 POUNDS PER SQUARE INCH GAUGE, ADMIXING WITH SAID PREHEATED GASEOUS HYDROCARBON FRESH GASEOUS HYDROCARBON AND OXYGEN, AND THEREAFTER SUBJECTING THE RESULTING MIXTURE TO THE AFORESAID OXIDATION REACTION, WHEREBY THE RATIO OF FORMALDEHYDE TO ACETALDEHYDE PRODUCT IS INCREASED. 